If you are running Google Adwords, there's a good chance that you haven't been able to resist searching with your target keywords to see if your ad shows up, where and how it looks.

You have probably come across a situation where your ad doesn't show up – either it doesn't show up no matter what you search for, or it shows up for some phrases and not others, or perhaps you are getting anedotal comments that you're 'not there'.

And so naturally, you become concerned that something is wrong. But don't worry - there are legitimate reasons why this happens. Here are the most common....